Abstract
Increased use of engineered nanoparticles (ENPs) has resulted in their entry into municipal wastewater treatment plants (WWTPs) as their final sinks. However, the adverse impact of ENPs on the bacterial activity in the activated sludge WWTPs is not yet well understood, despite their increased release into such systems. In this study, the impacts on WWTPS associated with the disposal of zinc oxide (ZnO) ENPs was investigated using a simulated WWTP developed as per the prescribed Organization for Economic Co-operation and Development (OECD 303A) specifications. Analyses were done to determine zinc concentrations at various stages of the setup, mainly in the raw wastewater and treated effluent, using inductively coupled plasma optical emission spectrometry (ICP-OES). The results obtained indicated low levels of zinc residue (about 50-200 μg/L) in the treated effluent compared to relatively high concentrations of Zn in the sludge (about 3 000 mg/kg). Results reported herein imply precipitation of ZnO ENPs during wastewater treatment processes and hence its high levels in the sludge. The presence of solid Zn in the sludge was determined using X-ray diffraction spectroscopy (XRD). Overall, no significant impact of ZnO ENPs on the performance of the simulated WWTP was observed, in terms of the removal levels of chemical oxygen demand (COD) during the treatment process.
Highlights
Biological wastewater treatment processes employ a consortium of heterotrophic and autotrophic bacteria, essentially to degrade organic matter present in wastewater
The chemical oxygen demand (COD) removal results suggest that dosing the influent with zinc oxide (ZnO) engineered nanoparticles (ENPs) had no significant adverse impacts on the overall treatment efficiency of the stimulated wastewater treatment plants (WWTPs), which is in agreement with earlier studies (Hou et al, 2013; Tan et al, 2015), especially at low dosing concentrations
Our results indicate that the release of zinc ions into the treated effluent exhibited a linear increase as the dosing ZnO ENPs concentration increased
Summary
Biological wastewater treatment processes employ a consortium of heterotrophic and autotrophic bacteria, essentially to degrade organic matter present in wastewater. The sorption of pollutants on activated sludge is among the fundamental processes for the removal of toxic substances including metals, synthetic organic chemicals, suspended solids, and pathogens in wastewater (Dobbs et al, 1989; Musee et al, 2007; Sheng et al, 2008). The advent of nanotechnology has resulted in fast production and wide usage of engineered nanoparticles (ENPs) in consumer products and industrial applications. This has led to unintended release of ENPs into environmental systems at different stages of their product life cycles (e.g. manufacturing, use, etc.) (Koehler et al, 2008; Musee, 2011). Zinc oxide (ZnO) ENPs are incorporated in numerous products including sunscreens, paints, cosmetics, dye-synthesized cells, plastic additives, catalysts and electronics (Woodrow Wilson, 2009; BCC Research, 2012; Piccinno et al, 2012); which in turn could lead to their release into natural and technical systems, e.g., wastewater treatment plants (WWTPs)
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